GB1015658A - Radiation source - Google Patents

Abstract

1,015,658. Optical apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 6, 1964 [May 20, 1963], No.18758/64. Heading G2J. [Also in Divisions G1 and H3] A source of radiation in the far infra-red, i.e. 10-1000 microns, is produced by directing coherent light 40, 42 from two lasers 22B, 24B on to the surface region 18 of one conductivity type, delineated by electrodes 14, 16, of a high mobility semi-conductor crystal 10, the frequency of the resultant radiation 30 being the difference between the frequencies of beams 40 and 42. A source 20 is connected across electrodes 14, 16 to produce a field of 2, 000 volts per centimetre. The beams 40, 42 may be reflected or refracted so as to approach the crystal along the same path, Figs. 1 and 2 (not shown), in which case the resultant radiation is at the angle corresponding to crystal 10 being a plane reflector. If however the beams 40, 42 have different angles of incidence the resultant beam 30 does not traverse path 46 corresponding to the angle of reflection for an incident beam 44, the mean of beams 40, 42, incident upon a plane reflector, but beam 30 is as shown nearer the normal to crystal 10 if laser 24B has the higher frequency and more distant than 46 from the normal if laser 24B has the lower frequency, a construction for obtaining the exact direction being described with reference to Figs. 4 and 5 (not shown). This characteristic may be used to measure angles, for an angular rotation of crystal 10 is amplified in the angular movement of beam 30. Alternatively the position of one of the lasers may be changed. It also follows from the angular relationship of beam 30 to beams 40, 42 that if the two input beams approach the crystal along the same axis but one beam has parallel components and the other convergent or divergent components the output beam will be convergent or divergent respectively, which means that lens elements need not be inserted in the beam 30 of far infra-red radiation but can be inserted in beams 40, 42 of optical radiation. The lasers 22B, 24B may be different lasers, a single laser operating at two different frequencies or two identical lasers operated at different temperatures to produce different frequencies. If the dimension of surface 18 is half a wave length of radiation 30 the total power emitted is an optimum, but if it is several times such wavelength beam 30 is highly collimated.